Precast Reinforced Concrete L-panel for Roofing
1995 Edition

The standard specifies L-panel lengths ranging from 1200 mm to 3900 mm, widths between 300 mm and 900 mm, rib depths from 80 mm to 150 mm, rib widths of 40 mm to 70 mm, and flange thickness typically around 30 mm. Panel overlap is designed between 80 mm and 150 mm, depending on climate conditions. Reinforcement bars have diameters from 6 mm to 10 mm. Channel units share similar dimensions but incorporate double the tensile reinforcement in ribs compared to L-panels. Mild steel bars are used up to 6 mm diameter, while larger diameters employ high strength deformed bars. These dimensional and reinforcement specifications ensure structural stability and proper weather sealing.

For concrete, M15 grade is suggested for standard environments, while M20 grade is preferred for regions with higher rainfall or aggressive atmospheric conditions. Reinforcement should use mild steel bars Grade I as per IS 432 (Part 1):1982 for bars up to 6 mm in diameter, and high strength deformed steel bars complying with IS 1786:1985 for larger diameters. All materials must conform to IS 456:1978 standards regarding strength and durability. Reinforcement bar sizes and cover are to be designed following IS 14242:1995 or as indicated in the standard’s tables to ensure adequate structural performance.

Deflection recovery testing involves selecting a minimum of three L-panels and one channel unit that have passed dimensional checks. These are assembled as a roof over masonry walls with a 75 mm bearing supported by 6 mm steel plates on walls sloped up to 1:10. The bearing gaps are filled with 1:2:4 concrete or equivalent mortar. Design dead loads are applied uniformly using loading blocks, and mid-span deflections are measured with a dial gauge of least count 0.02 mm or less. After removing the load for 24 hours, the panels must recover at least 75% of the deflection under load to pass. Failure load testing, conducted only on units passing deflection recovery, applies uniform load via loading blocks or hydraulic jacks to assess structural capacity. Loading blocks are carefully positioned to prevent arching effects, and this is typically a type test for new or modified designs.

Sampling is performed by randomly selecting 5 L-panels and 5 channel units for lots of 300 units or less. For larger lots, 5 samples per 200 units or part thereof are taken, following IS 4905:1968 sampling procedures. A batch is accepted if at least 4 out of 5 samples conform to dimensional requirements; otherwise, it is rejected if more than one fails. Routine tests include dimensional verification and deflection recovery, while failure load testing is reserved for new designs or changes. This statistical sampling ensures consistent quality and compliance with the standard.

Panels should be transferred to curing yards between 48 to 60 hours after casting, depending on ambient temperature and humidity. Throughout handling and transportation, panels must be kept in a vertical orientation to prevent bending or cracking. Any paper used during casting should be removed while still wet to avoid surface damage that occurs if paper dries and adheres strongly. Proper clamps and supports must be employed during all stages to prevent warping or distortion, thereby preserving the panel's structural integrity and surface finish.